Step-guided etching toward aligned MoS2 nanoribbons

Abstract

Fabricating aligned arrays of hexagonal transition metal dichalcogenide nanoribbons is essential for high-density integrated devices but remains challenging due to the intrinsic lattice symmetry, which typically favors multi-directional orientations. Here, we report a step-guided anisotropic etching strategy that exploits the reconstructed steps of annealed c-sapphire substrates to overcome this symmetry constraint, yielding unidirectional MoS2 nanoribbon arrays. This process achieves precise orientation control while preserving the high crystallinity of the parent film. Crucially, angle-resolved spectroscopic investigations reveal a striking decoupling between the linear and nonlinear optical responses in these one-dimensional nanostructures. While polarized Raman spectroscopy confirms a strain-free lattice with isotropic phonon response, second harmonic generation measurements uncover an anisotropy governed by the one-dimensional confinement and strong depolarization field effects. Our findings not only establish a top-down pathway for orientation-controlled nanomanufacturing but also highlight the potential of geometric engineering in tailoring nonlinear light–matter interactions, enabling polarization-sensitive functionalities.